Transmission monitoring system



Nov. 7, 1944.

N. BOTSFORD TRANSMI S S ION MONITORING SYSTEM Filed Jan. 28, 1941 FIG.

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MONITOR Rec.

INVENTOR By N. BOTSFORD ATTORNEY Patented Nov. 7, 1944 UN E STAT MTE T OFF C =2 362,s4s e 1 r TRANSMISSION MONITORING SYSTEM Nelson Botsford, Rutherford, N. .l., assignor to Bell Telephone Laboratories, Incorporated, New I York, N. Y., a corporationof New York, I Application January as, 1941, Serial No. 376,362 I "sola ms. (o1. rig-175.3)

This invention relates to monitoring systems and more particularly to such systems for use at the input of the amplifier, over contacts of relay 501, and the open-wire line H3, and the other cable line H2, are connected to the output ofgthe amplifier over contacts of relays 503 and 50!, respectively. f

In general, open-wire lines require a higher level of transmission than do cable linesof the type employed in this service, and therefore the lines receiving a program are connected to taps on an autotransformer' (5H), across the output circuit of the amplifier, which taps are so chosen as to provide the desired levels. In practice, the

open-wire lines (H3 for example) are connected across the entire winding of the autotransformer Whereas the cable lines (H2 for example) are connected to intermediate taps as discussed in the patent specification and shown in the drawing.

In systems of the character above described it is desirable for an attendant to monitor, i. e., listen to the program being repeated to the outgoing lines and this is accomplished, in practice, by automatically connecting the monitoring circuit to the high level output of the amplifier when an open-wire line is connected to its input and when a cable line is connected to the inputoi the amplifier, the monitoring circuit is connected to the lower level output. As it is desirable to maintain a substantially constant level of transmission energy in-the monitoring receiver, re-

gardless of the energy level supplied to the monitoring circuit, an .object' is to provide means whereby this result is accomplished. in a simple work comprising a plurality of inductive andnoninductive resistance elements, said network having two input terminals arranged to be connected to the high level of two energy sources, and having two output terminals permanently connected to a monitoring receiver, said output terminals being also adapted to be connected to the lower level of said two, sourcesalternatively with the connection'of the input terminals of the high level source, said network elements being so arranged and connected that when the higher level source is connected to the input terminals of the network a predetermined lower level of energy will be applied to the receiver and, alternatively, whenthe lower level source is connected directly to the receiver, and consequently to the output Connected across the outputof the amplifierxis an autotransformer 2 having, outer terminals 3, 4 and intermediate terminals 5, 6 which sets of terminals 3, land 5, .6 serve as separatesources of different energy level, the energy level across terminals 3, 4 being higher than the level of energy across terminals 5, 6. A monitoring receiver R is shown having an input circuit IN' with" which a transmission loss network, or pad, -1 is permanently connected, which loss pad has two sets of terminals 8, 9 and l I], l l whereby the receiver input circuit INcan be alternatively connected either to the high level terminals'3, 4 of the autotransformer 2 or t the low level terminals 5, 6,

The loss pad I, in practice, consists of a transformer having four windings [2, [3,14 andv l5 connected in series-aiding relation and having a non-inductive resistance 16, connected between windings i3 and M. When the high level terminals 3, 4 of the autotransformer Zare con.-

nected to terminals H], H of the loss pad 1 the voltage impressed across the receiver B may be controlled by the proper proportioning of the turns of windings l2, I5 and I3, I4 and the value of resistance l6,'while at the same'time the impedance looking into terminals I0, I I of the pad may be maintained equal to the impedance of the receiver R.

When the terminals N, H of the loss pad are disconnected from the high level source and terminals 8, 9 are connected to the lower level terminals 5, 6 of transformer 2, current flows directly to the input circuit 1N and thence to the receiver R with the combined inductance and resistance of the pad combination in shunt thereto. Under this condition the non-inductive resistance of the pad element is in series with the series-aiding inductance of the windings l2, l3, l4, [5 which, depending on the design of the transformer, may be so high that its shunting effect on the input circuit is negligible. For example, ifthe impedance looking into the receiver R is 600 ohms and it is desired to maintain approximately this same impedance when looking away from either the high or low level terminals 3, 4 or 5, 6 and at the same time introduce an attenuation of approximately 6 decibels between the high level terminals 3, 4 and the receiver R, the pad I may consist of a transformer having four substantially equal windings the combined non-inductive resistance of which is '70 ohms, the series-aiding inductance of the windings 120 henries and the non-inductive resistance connected in seriesat the mid-point of the pad may have a value of 1800 ohms. Bychanging the ratio of the windings and the value of the resistance, the 690-ohm impedance may be maintained and the high level current, when connected, attenuated by any reasonable amount without substantially altering the low level current when the receiver is switched to this source.

Fig. 2 shows a practical application of the loss pad in a program switching system arranged to amplify and connect a program incoming over one line to one or more other lines which may require either a low or high level of transmission ener y, depending on the character of the individual line, for example, in the drawing LO represents a so-called open-wire line and LC a cable line which, as previously mentioned, require different levels of transmissionenergy for their satisfactory operation, i. e., open-wire lines when receiving a program from the network for transmission to a distant station require a higher level of transmission energy supplied thereto, due to line noise, etc., than do cable lines which are not subject to as much interference of this character.

For purposes of description the switching and amplifying arrangementof Fig. 2 is shown in the condition where the open-wire line L is supplying the program, originating at some distant station, which line is connected, under control of a simplex switching circuit 20, to the input of amplifier A over contacts 21 and 22 of operated relay 23, and cable line LC is connected to low level terminals 5, 6 of an autotransformer 2 across the outputof the amplifier over contacts 24, 25 of relay 26. Under this condition, the intermediate terminals or taps IO, M of the loss pad I are connected over contacts 21, 28 of relay 23 to the high level terminals 3 4 of transformer 2 whereupon loss pad 1, as before described, introduces a desired loss in the monitoring circuit.

Now assuming the case in which the cable line LC is supplying the program for distribution to the network then relay 26 will be operated and all other corresponding relays including relay 23 will be released whereby cable line LC is connected over contacts 29, 30 of relay 26 to the input of amplifier A and open-wire line L0 is connected over contacts 3|, 32 of relay 23 to the high level terminals 3, 4 of autotransformer 2 across the output of the amplifier thus supplying the full output energy of the amplifier to the open-wire line. Under this condition with relay 26 operated, the circuit of the monitoring receiver R is connected over contacts 33, 34 directly to A the low level terminals 5, B of transformer 2 and due to the high series-aiding inductance of the coil windings l2, l3, l4 and N5 of pad 1 plus the non-inductive resistance IS the shunting effect of the pad on the low level energy applied to the receiver R is negligible.

What is claimed is:

1. In a monitoring system, two sources of signal frequency of different energy level, a receiver having an input circuit adapted to be connected to either source, means for maintaining a constant voltage level across said receiver regardless of which source the input circuit is connected to, said means comprising an impedance including a pair of mutually inductive transformer windings and a non-inductive resistance in series 'therebetween connected in shunt to said input circuit, and means for connecting said lower level source directly across said impedance and for connecting said higher level source between intermediate points of said pair of transformer windings.

2. In a monitoring system, two transmission lines operating at difierent energy levels, a monitoring receiver, means for connecting said receiver to the higher energ line, and other means for connecting the receiver to the lower energy line, said first means including an impedance in shunt to said receiver, effective to attenuate the energy of the higher level line by an amount equal to the difference in level between the two lines when a connection is established between said higher level line and two intermediate points in said impedance, said impedance having no substantial attenuating effect on the energy applied to the receiver when it is connected to the lower level line by said second means.

3. In a monitoring system in which a receiver is connected to either of two sources of different level signaling energy, meansfor equalizing the energy level applied to the receiver regardless of the source to which the receiver is connected, said means comprising an impedance network including inductive and non-inductive elements connected in shunt to said receiver, a circuit including certain of said elements in series therewith and other of said elements in shunt thereto for connecting said receiver to the higher energy source and a second circuit in parallel with said network and receiver for connecting to the lower energ source,

4. In a monitoring system, two sources of signaling frequency of different volume level, a monitoring receiver having an input circuit of impedance Zr; a network having two input terminals and two output terminals, said output tenninals being connectedto the input circuit of said receiver, means for alternatively connecting said high level source to said network input terminal or the lower level source directly to said receiver input circuit, said network comprising a plurality of impedance elements of such value and so arranged that energy transmitted from said higher level source to the input terminals of said network is attenuated a predetermined amount, the impedance viewed from the output terminals of the network is substantiall that of the receiver im edance. Zr, and the impedance of the network viewed from its input terminals is also substantially that of the receiver Zr.

comprising a serially connected plurality of mutually inductive transformer windings and a noninductive resistance, a load circuit having a known impedance in parallel with said network, a low energyinput circuit connected in parallel with said network and loadand a high energy input circuit connected to said network intermediate the points of connection of said load circuit thereto, the constants of said network being 50 chosen and said high energy input circuit so connected to said network that energy transmitted by way of said high energy input circuit to the network and load is attenuated a predetermined amount, the impedance of said network and load as seen from saidhigh-energy circuit is substantially equal to said load impedance and, alternatively, the impedance of said network and load, in parallel, as seen from said low energy circuit is also substantially equal to said load impedance and without substantial energy attenuation due to said network when energ 'is trans one of said input circuits and the remainder of said inductive elements and said resistance seriallyconnected in shunt thereto and said network I being wholly connected in shunt to the second circuitgand means for alternatively connectin said receiver to the high level line by way of the first input circuit or to the low level line by way of the second input circuit, said network being so constructed and its constants so chosen that the level of transmission applied to the receiver is substantially the same regardless ofwhich line network having a portion thereof in series and another portion in shunt to a first one of said input circuits and wholly in shunt to the second circuit, and means for alternatively connecting said receiverto the high level line by way of the first input circuit or to the low level line by way the receiver is connected to.

age attenuation through the network to trans mission applied to the line on the other side of the network.

1 9. In a monitoring system, two sources of audible frequency of difierent power level, a'monitoring receiver, an input circuit for said receiver;

means for connecting said input circuit to either source and static means for maintaining a con:

stant impedance and power level across said in-v put circuit regardless of the source tOWhich said I inputcircuit is connected, said static means comprising an impedance including a pair of inductive elements and a non-inductive element connected in series across said input circuit, and said. means for connecting the input circuit to the lower power level source comprising a connection in parallel with said impedance and" the means for connecting the input circuit to the higher level source comprising a connection in shunt to a portion of said impedance including said non-inductive element and substantially half of each inductive element. NELSON BOTSFORD; 

